Preserve Windows task results

[attahn]

Windows task joins were replacing completed task results with NULL because the native pthread shim cannot return a thread result.

This keeps the result on MakoTask, documents its publication contract, and makes six task and timed-join suites blocking on Windows.

Verified with 78 Rust tests, focused Windows and WSL/Clang runs, and the full Windows suite improving from 304 passed / 59 failed to 334 passed / 29 failed.

Summary by CodeRabbit

• Bug Fixes

  • Preserved task return values when joining native Windows worker threads.
  • Improved task awaiting behavior on Windows, including timed waits.

• Tests

  • Expanded Windows runtime test coverage for actors, worker tasks, typed joins, function calls, and wave queues.

• Documentation

  • Updated the unreleased changelog with the Windows task return value fix.

[attahn]

@coderabbitai[bot] review

[coderabbitai]

📝 Walkthrough

Walkthrough

The runtime adds a join wrapper that prevents native Windows thread joins from overwriting stored task results. Await paths use the wrapper, the task result contract is documented, Windows CI runs additional tests, and the changelog records the behavior.

Changes

Windows task result preservation

Layer / File(s)	Summary
Join result handling runtime/mako_rt.h	The task result is documented as read-only after completion, and mako_task_join_thread joins threads without storing the pthread return value.
Await integration and validation runtime/mako_rt.h, .github/workflows/ci.yml, CHANGELOG.md	Non-pooled await paths use the new join wrapper; additional Windows test programs run in CI, and the runtime behavior is documented in the changelog.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: loreste

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: preserving task results on Windows during task joins.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

@attahn: I’ll review the changes in #13.

✅ Action performed

Review finished.

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[attahn]

CI is green except for the strict 1.5x benchmark gate. This run measured slice100k at 1.70x and map50k at 2.31x; the preceding green run measured the same cases at 1.08x and 0.95x. This change does not touch benchmarked code, so the failed job should pass on rerun.